Recently, in a food packaging, a gas-substitution packaging has been carried out which substitutes an inert gas for air surrounding food within a container before packaging in order to prevent food from being denatured or deteriorated due to oxygen.
Inert gases used for the above-described gas-substitution packaging are normally nitrogen or carbonic gas, and rarely a mixture of both the gases. This is effective in suppression of aerobic bacteria of the packaged food, retention of effective components, rancidity prevention, discoloration prevention, mold prevention and the like.
A conventional gas-substitution packaging has been carried out by inserting a packaged container filled with a content into a chamber capable of being closed, once making the interior of the chamber vacuous to remove air in the packaged container, thereafter blowing an inert gas into the chamber to fill a head space of a container with the inert gas, and sealing an opening of the container within the chamber.
Alternatively, a method has been carried out which comprises the steps of directly blowing an inert gas against an opening of a container being conveyed by a conveyor without producing a vaccum and deaeration, and substituting the inert gas for air within the head space.
In the above-described gas-substitution within the chamber, the inert gas is blown into the chamber after the latter has been once formed into vacuum, and therefore, it takes time, with the result that work efficiency is poor. Furthermore, since the inert gases are filled into the chamber every time, a large quantity of inert gases are required, resulting in a great loss of inert gases. Moreover, when the aforesaid conventional method is applied to a lateral type filling and sealing machine for a molded container which automatically carries out the step of filling a molded container with a content and sealing a cover, it is necessary to open and close the chamber as the conveyor conveying the molded container moves, position a conveyor portion on which the container is placed into the chamber to seal when closed. Therefore, there gives rise to a drawback in that the apparatus becomes complicated and expensive.
Alternatively, the method for directly blowing the inert gas without producing vacuum and deaeration to carry out gas-substitution poses problems in that not only the inert gases escape into atmosphere, increasing a loss of gases but also it is difficult to enhance the gassubstitution rate.